When copying a dvd, copying freezes at (for instance) 33%.
On the data (shiny side) of the disk, where on the disk would 33% be??
There is more data closer to the outer edge, (bigger circles=more data)
If one knows where 33% location is on disk, one knows where (approximately) to look for scratches to buff out, rather than buffing the whole disk.
-corne-